Manufacture of hollow glass or other thermoplastic articles is a very ancient and well known art. The necessity of modern mass production of certain glass articles, caused the advent of the modern automated glassware forming machines, which have acquired extended preference to carry out the normal procedure to form glassware, in contrast to the slower and quite less efficient process of forming such articles by hand. In broad terms, however, all the modern mass production machines require to carry out a rather large and intricate plurality of sequential operations in order to form glassware from a continuous supply of molten glass gobs, whereby they require a suitable timer device to sequentially and timely carry out the said operations in the machine.
Broadly speaking, a process of machine forming hollow glass articles comprises sequentially feeding glass gobs to a plurality of forming sections of the machine, and sequentially controlling the performance of each individual forming section of the machine in order to carry out the following operations: Glass gobs from the gob generating means are conducted by means of scoops which are alternately placed under the glass gob source and deliver the gobs to a set of feeding channels leading the gobs to the interior of blank forms located at a blank forming station; thereafter respective parisons are formed within said blank molds by means of an operation selected from a pressing operation by working pistons into and out of the blank forms, and a blowing operation by working a baffle and thereafter counter-blowing the gob through the bottom of said blank mold. Once the parison has been formed in the blank mold, the latter is removed from the blank forming station in order to release the parison formed and a reheat and stretch period of the parison is permitted in order to increase the temperature of the cooled surfaces of the parison at the expense of the heat preserved in the interior of the body of said parison until the parison is at a uniform temperature. During this operation and thereafter, the parison remains supported by means of a neck ring which may at the same time be a mold for forming the neck of the finished article. Thereafter, a pair of open blow mold halves are closed around the thus formed and reheated parison either at the blank forming station or by firstly transferring and inverting the parison from the blank molding station to the blow molding station, depending on the type of machine utilized, and the blowing of the article is commenced in order to finish the ware.
Once the parison or the split blow mold containing it is removed from the blank molding station and transferred to a second station which may be a blow molding station or a take out station, the blank molding station is left free to commence operation again by returning the blank mold into position to receive a second glass gob and meanwhile the finished article is removed by opening the blow mold halves and placing in the appropriate position a take out mechanism, whereafter the neck ring is opened to deposit the article onto said take out mechanism which takes the finished ware out of the machine by means of a conveyor or the like.
Additional operations may be necessary for each forming section of the machine if the same operates on the paste mold process, inasmuch as in this particular instance, once the blow mold halves close around the parison, the neck ring commences rotation in order to blow and rotate the parison until the finished ware is completed. Also, cooling of the blow mold halves which are not in operation becomes necessary in order to reduce their temperature which is generally raised by the hot parison and, therefore, showers to spray a cooling liquid are generally provided in this type of glassware forming machines, in order to spray said fluid on the interiors of the blow mold halves when the same are not in operation to blow an article therein, in order to attain appropriate cooling or humidification thereof, the latter being necessary when using the paste mold method and the former being necessary when using the hot mold method.
As it can be seen from the above, the rather intricate and accurately sequentially timed operations required for each of the forming sections to be performed, cannot be controlled by hand and, therefore, it has been customary up to recent times to provide a mechanical timer device in the machine, to work in conjunction with a plurality of cam operated valves each one handling an appropriate fluid to actuate fluid operated motors that in turn actuate every single mechanism of the machine. In other words, all modern machines are designed to have fluid operated mechanisms in order to be controlled by a set of valves which are in turn controlled by means of the mechanical timing device.
The most widely used mechanical timing device is the very well known mechanical timing drum comprising a rotary drum having a plurality of circumferential grooves on its surface, within which a corresponding plurality of cams are arranged in positions suitable to timely actuate cam followers associated with cam operated valves to sequentially and timingly operate all the mechanisms of the machine as stated above.
The prior art timing drum is generally rotatably driven in synchronism with the gob feeding means and with the take away conveyor for finished articles, thus resulting in a somewhat continuous flow of molten glass gobs into the machine and a corresponding flow of ware down the take away conveyor.
As the timing drum associated with a given section rotates, the several fluid operated forming means, including the aforementioned blank and blow molds and the elements associated therewith, are mechanically actuated in the required sequence as determined by the relative positioning of the cam members in the grooves provided on the surface of the timer drum, in response to the application of fluid pressure thereto under the control of the valves which are opened and closed by the cams.
Being therefore the sequential operation of the different elements of the glassware forming machine controlled by the positions of a plurality of cams arranged in a corresponding plurality of grooves circumferentially extending on the surface of the timer drum, it is quite obvious that the timing operation cannot be considered as very accurate, because being the cams adapted to be adjustably positioned in their respective axially spaced grooves at points on the drum surface which coincide with the position of respective valve operating members at the times at which such valves are to be operated, when said cams are positioned, normally by the tightening of nuts or the like, said positioning of the cams on the timing drum is an inexact procedure at best when the drum is stationary, but it becomes a time-consuming and painstaking task to locate and secure the cams with any degree of accuracy when the drum is rotating.
While the cam position may be more or less accurately adjusted with the drum stationary at the start of a run, it is generally necessary to adjust the position of said cams when the machine is operating, in order to secure an efficient function of the mechanisms of the machine. It is generally undesirable to stop a machine during a run to permit adjustment of a cam, since, as is well known in the art, glass forming machines desirably achieve and maintain a thermal balance upon continued operation, and therefore sometimes it becomes necessary to carry out adjustment of certain cams when the machine is working and thus the drum is rotating. On the other hand, even if the operator succeeds in loosening the clamp or nut of the cam, repositioning the cam as accurately as possible and retightening said clamp or nut, continuous use of the timing drum and the cams causes mechanical wear of the cam surface or of the follower associated with the valve member that operates the cam operated valve, whereby such wear sometimes delays the operation of the valve to a significant degree, resulting in irregularities in the forming operation and resultant production of rejects and unacceptable ware. Finally, the worn cam surfaces may ultimately fail to actuate the cam follower operating the valve, whereby the operation of the machine will no longer be satisfactory for carrying out the process for manufacturing glassware.
In an effort to avoid the aforementioned problems, electronic control systems have been devised in the past, by providing electronic circuits and counters for determining the number of degrees of rotation associated with each operation of a glassware forming machine, to accurately proportion the duration of said operations and the sequence thereof, so as to avoid the mechanical failures of the cam members of the very well known mechanical timing drum.
Thus, for instance, in U.S. Pat. No. 3,762,907 to Quinn et al., patented Oct. 2, 1973, an automatic electronic control system is disclosed which controls and maintains the sequence of events constituting the various steps of ware formation with a degree of accuracy unobtainable by the mechanical timing drum. The sequential timing of the operations of each forming section of the machine, in accordance with the above mentioned patent, is accomplished by means of a timing pulse generator located on the drive shaft of the machine, which generates one pulse for every degree of rotation of the shaft, while a reset pulse generator is also mounted on said drive shaft for generating one pulse for every 360.degree. of rotation of the shaft, in order to reset the control for commencing a new cycle of the machine. Said control contains electronic circuitry and memories to store sufficient information to carry out in sequence the different operations of each section of the machine. By this means, the timing of the operation of a function may be altered by the mere manipulation of a switch, such as a thumbwheel, as opposed to the somewhat cumbersome procedure of adjusting timing cams as was necessary in the prior art mechanical timer drum.
The sequential timing pulses and the reset pulses which are generated by the pulse generating means under the influence of the rotation of the main shaft, are taken to a sequence distributing circuitry in order to distribute the sequential and reset signals to the plurality of individual forming sections contained in the machine, and the electronic control system in accordance with this patent also contains emergency stop means as well as programmed stop means for each section of the machine, that enable emergency stop of all the mechanisms of the machine or alternatively, a programmed stop in which the related machine section will proceed automatically through a sequence of events required to place the several elements in a safe position and ready for access to the operator.
The electronic control system disclosed in U.S. Pat. No. 3,762,907, however, represents a mere replacement of the mechanical timer drum and in essence acts in much the same manner as said timer drum, inasmuch as what this electronic system accomplishes is the mere replacement of the cams of said mechanical timer drum by electronic modules or circuits and the sequential programming of the electronic system is practically the same as the sequential positioning of the cams in the grooves of the timing drum. On the other hand, while this electronic control system is capable of changing or shifting the timing of relative variables, and it may be easily concluded that relative variables (that is, timing of operations that are computed as a proportion of the duration of the cycle) may be accurately shifted with the selection of a position of a predetermined number of switches, it may also be easily concluded that the handling and changing or shifting of absolute variables (that is, duration of operations which are independent of the duration of the total cycle) can hardly be accomplished, because this control system is not equipped to effect such changes and even if it were, there is no way of testing the new times selected by the operator and there is no way of knowing in advance if the times selected are correct in order to prevent cutting down certain variables that cannot be decreased or lenghtening other variables that cannot be increased, in order to coordinate them within the total duration of the cycle.
In other words, if the absolute times selected by the operator are not accurate and proper, then this must be learned the hard way, because said mistakes cannot be detected until the machine commences normal operation and the thus formed goods are determined to be defective.
On the other hand, in glassware forming machines there are certain operations that have been considered highly critical, such as the time in which a glass gob is cut and delivered by the glass gob feeding and distributing means, the time when the glass gob released by the glass gob feeding and distributing means falls within a blank mold and the time when the blank forming operation commences, that is, when the blowing or the pressing of the gob is started. It may well happen that a glass gob is not properly cut and therefore the blank mold does not receive the appropriate load to work on and it also may happen that the scoops and guiding channels lose the glas gob along their length for certain reasons or it may also well happen that the glass gob takes an extremely long time to fall down into the blank mold, and these failures, if not properly detected, may cause a highly defective operation of the machine.
The remedies to these faults are rather simple to achieve, inasmuch as it may merely take lubrication of the scoops and channels or it may take the mere cleaning of the shear that cuts the glass gobs, in order to accomplish an appropriate and perfectly timed operation of the machine. On the other hand, if the blank forming operation does not commence at the appropriate time after the glass gob has fallen into the blank mold, then the very well known "settle-wave" defect appears in the parison; and also the remaining sequence of steps, and particularly the reheat and stretch operation, cannot be carried out properly because a delay in commencement of the blank forming operation, may cause a corresponding and unadmissible reduction in the time allowed for this reheat and stretch operation in the machine.
The electronic control system in accordance with U.S. Pat. No. 3,762,907, does not contain any means to accurately control these highly critical operations, whereby it has left much to desire and may be considered as a mere improvement over the mechanical timing drum, in the sense that, using exactly the same principle of said mechanical drum, it has replaced the timer cams and cam followers which actuate cam operated valves, by a set of electronic circuits which actuate on solenoids that in turn actuate electrically operated valves. Otherwise, it may be said that the above systems are exactly the same, with the only advantage that the electronic system of Quinn et al. is not subject to such a drastic mechanical wear as is the mechanical timing drum, in view of the fact that the latter uses cam surfaces and cam followers which may wear out in time.
Another slightly different type of electronic control system for glassware forming machines is disclosed in U.S. Pat. No. 3,877,915 of Dudley et al., patented Apr. 15, 1975. This patent discloses an electronic control system which operates on the basis of determining the duration of certain modes of operation within the cycle and also depends on a counter counting degrees or fractions of a degree, for providing a preset count to be compared by means of a computer with an actual count, in order to actuate the different mechanisms of the machine when both counts are equal. This electronic system also provides for the possibility of manually altering the boundaries of each mode by predetermined increments to improve the machine efficiency at the press of a button. The related machine functions are automatically revised as required in accordance with the preset program and the selected change is automatically cancelled if any of these functions is outside of predetermined limits.
By providing a computer which compares, as mentioned above, two inputs, that is, the current total count shown by a counter and the preset count stored in a table of settings subprogram, and by providing means for rejecting any setting or resetting of the boundaries corresponding to each of the modes of operation in which the cycle is divided, whenever this setting or resetting is effected by manually operable means, such as the very well known thumb wheels for example, or in other words, by the provision of a subprogram contained in each unit of operation which will determine whether the proposed change of the duration of relative functions will exceed predetermined limits set for it, the control system of U.S. Pat. No. 3,877,915, solves the problem of having to take the risk of operating the machine with reset functions and thus avoids the problems caused by the electronic circuit of U.S. Pat. No. 3,762,907, in the sense that the electronic system itself will not accept any change in the functions which will not be within the boundary limits of each of the modes of operation in which the complete cycle of the forming unit has been previously divided by the main program fed into and stored in the computer.
In other words, when it is desired to change the timing or the duration of certain functions of the elements of the machine to accomodate for a run of a different type of glassware, then the operator may manually change or shift or reset said functions, but the computer will not accept the changes if they do not fit with the duration provided within the cycle for each of said modes of operation within the boundaries previously fixed for each said mode of operation, thus warning the operator that the degree signals fed to the computer are not correct and that, therefore, a new resetting must be made.
However, still with this remarkable improvement over the prior electronic control systems for glassware forming machines, the control system of U.S. Pat. No. 3,877,915 is still somewhat inefficient in the sense that, even when it provides for the rejection of a certain resetting of variables that have been manually entered by the operator, thus warning the operator that the degree signals fed to the computer are not correct, it does not furnish the operator with a clear indication as to where the error must be located, whereby the operator must test several different resettings until the computer accepts one of them to operate under the new timings (measured in degrees of rotation) that are necessary for a new run. This undoubtedly, is a definite drawback of the electronic system of U.S. Pat. No. 3,877,915.
Also, the above described electronic control system does not provide for signal feedback into the same, in order to suitably control the most critical functions of the forming sections of the machine, for instance, the glass gob cutting operation, the passage of the released glass gob out of the guiding channels and into the blank mold, and the commencement of the blank forming operation, whereby the same comments stated above in connection with the electronic control circuit of U.S. Pat. No. 3,762,907 fully apply.